U.S. sales of medium- and heavy-duty trucks rose 17.3% last month, making it the best September since 2006, WardsAuto data shows.

All weight classes for groups 4 through 8 combined experienced gains over like-2012, with every manufacturer recording year-over-year sales increases.

Class 8 led the way, as heavy-truck sales posted a 21% rise in year-over-year sales with deliveries of 16,125 units. PACCAR’s Kenworth brand saw September sales rise 49% and Volvo truck brands Volvo and Mack posted increases of 34.7% and 24.7%, respectively.

Freightliner’s share of the Class 8 market dipped slightly to 33.8% from last year’s 35.8%, but still remained in a solid position as the sales leader. Kenworth was a distant second with a 16.9% share, while International held 15.5% and Peterbilt was at 11.8%. Volvo rounded out the top five at 11%.

Class 7 sales for the month totaled 3,638 units, 12.5% above year-ago results, as most companies enjoyed solid gains except for Ford (-41.4%) and International(-15.2%). Gainers included Hino (+75.9%), Peterbilt (+70%), Kenworth (+34.8%) and segment leader Freightliner (+31.4%).

Overall Class 6 sales were up 27% over September 2012 due to gains by Freightliner and Hino and a 172% increase for Peterbilt. International and Kenworth posted substantial declines in Class 6 with year-over-year losses of 37.6% and 20.4%, respectively.

International, Freightliner and Isuzu led the way in Class 5 with deliveries rising a modest 1.9%. Ford was the only manufacturer to post a drop, with sales falling 16.9%.

The 31.2% climb in Class 4 deliveries was the best performance last month among any big- or medium-truck group, as sales of Isuzu’s new domestically built walk-in van drove sales up 80.9%.

Despite September’s promising results, year-to-date sales of medium- and heavy-duty trucks in the U.S. were off 2.1% from the same period year-ago at 254,004 units. Class 8 sales were down 9.6% at 132,593 units, with the industry forecasting flat results for the rest of 2013. Full-year 2013 sales are expected to drop slightly to 183,000 units, about 6% lower than 2012’s mediocre 194,715 tally.

Medium- and heavy-truck inventory fell in September to its lowest level since April, as overall days’ supply was at 61, continuing a recent trend.

Class 8 had 35,287 units in stock at the end of last month, a 50 days’ supply and the lowest this year. That compared with 39,955 units, or 69 days’, year-ago.

Medium-duty inventory of 40,844 units, a 75 days’ supply, was down from 40,077, or 83 days, in like-2012.

In other big-truck news:

  • The all-new Kenworth T880 is now available for order. Introduced at the 2013 Mid-America Trucking Show, the Kenworth T880 is especially suited for vocational customers who demand a durable and reliable truck, including dump, mixer, refuse and heavy-haul applications, Kenworth says.
  • The amount of freight carried by the for-hire transportation industry in the U.S. rose 0.4% in August from July, rising for the second consecutive month to reach the second-highest level in the history of the Bureau of Transportation Statistics’ Freight Transportation Services Index which goes back to 2000.